Why is my material solid white?
The texture coordinates cannot control the shader mix factor.

An image is not a shader so it shouldn't be connected to a shader mix.

The mix shader shouldn't feed a color to the diffuse shader...

What you need is the Texture coordinates to control how the image texture is mapped. (Ideally you should unwrap the object for proper texture placement and use UV coordinates... but you can use Generated while you learn to unwrap)

The dark and bright areas of the image control how the transparent and diffuse shaders mix.

The color for the diffuse shader determines the color of the clouds.



I suggest you watch the so-called "tutorial" over a few times to familiarize with the steps taken... Nodes do require a certain order as the results will be different depending on how they are connected.